Rebuilding Of Typical Microcontinents In The Eastern Part Of The North China Craton And Its Constraints On The BIF Mineralization

Craton is an ancient part of continental lithosphere,which can form a large-scale continent through a series of collision-orogen events.The ancient rocks in the craton preserved the growth and modification history of the early continental crust and were closely related to the mineralization of the ore deposits.A typical granite-greenstone belt and some large Archean BIF(Banded Iron Formation)-hosted iron deposits developed in the Eastern Block of the North China Craton(NCC).In this study,we systematically studied the Precambrian geological evolution of the NCC,the amalgamation process of microcontinents,and the mechanism of BIF-hosted iron deposits by using the methods of petrogeochemistry,deposit geochemistry and zircon Hf-isotopic mapping.Our study provides important insights for the key scientific issues,such as the BIF mineralization,and the formation of the Neoarchean-Paleoproterozoic continental crust.This study summarized zircon U-Pb ages,Lu-Hf isotopes and whole-rock geochemistry of the Archean to Proterozoic rocks in the Eastern Block of the NCC.The late Neoarchean to early Paleoproterozoic subduction-collision process was recorded in the Eastern Block of the NCC.During the subduction process,the hot mantle materials upwelling resulted in the formation of island arc basalts.The partial melting between the juvenile magma and the mafic crust formed the TTGs of volcanic arc series.The TTGs and amphibolites formed by the metamorphism of basalts indicate a large-scale crustal growth in the Eastern Block of the NCC.The subduction in the Eastern Block of the NCC is characterized by ocean-continent subduction and strongly volcanic activities.The crustal growth is characterized by juvenile continental crust,which is related to the reworking and recycling of ancient crustal materials.Our study provides a key issue for the continental crustal growth through the accretion and reconstruction of oceanic-arc terranes during subduction.Zircon Hf-isotopic mapping reveals the crustal growth and modification of the Eastern Block of the NCC.The Eastern Block of the NCC is composed of the Jiaoliao,Qianhuai,Xuhuai microcontinents,and the Yanlingguan granite-greenstone belt.This study suggests that the Neoarchean-Paleoproterozoic microcontinents in the Eastern Block of the NCC collided and amalgamated along the Yanlingguan granite-greenstone belt.All of them recorded the major Neoarchean-Paleoproterozoic magmatic events from 2800 to 2450 Ma.The microcontinents collided and amalgamated into a whole part at ca.2500 Ma.Rebuilding of microcontinents is of great significance for understanding the Neoarchean to Paleoproterozoic tectonic evolution and cratonization of the NCC,and provides an important basis for the initiation of plate tectonics.Based on the comparative study of typical BIF-hosted iron deposits in the Eastern Block of the NCC,this contribution proposes the metallogenic mechanism of the BIF.During the late Neoarchean to the early Paleoproterozoic,due to the crustal instability and plate-margin activities,the volcanic-hydrothermal system was formed by the mixture of high-temperature hydrothermal fluid and sea water under the subduction and crustal growth.The leaching of volcanichydrothermal fluid on the juvenile oceanic crust provided the source of Fe and Si,and the Archean anoxic paleo-ocean with negative Ce anomaly also provided a stable setting for the BIF sedimentation.The great quantity of Fe and Si elements precipitated to form the banded iron formations under the shallow sea and coastal sedimentary environment.The features of BIF mineralization in the Eastern Block of the NCC are characterized by absence of Superior-type,relationship with crustal growth and volcanism,being distributed in the granite-greenstone belt,and the strong metamorphism and deformation.Our study provides the basis for the prospecting of BIF-hosted iron deposits in the granite-greenstone belt and the theoretical basis for the mineralization of BIF.